Last summer, the Ebola outbreak in West Africa was all over the news. At the outbreak’s height, many health officials feared the disease would spread across the globe, and indeed individuals in the United States and Europe were diagnosed with the disease. However, cases outside of West Africa were kept isolated and a global outbreak of the disease was prevented.

Scientists have developed a method to deliver an oral vaccine using probiotics. The term probiotics refers to so-called “good” bacteria, such as Lactobacillus acidophilus and Lactobacillus casei, that prevent the growth of dangerous bacteria, aid in digestion, increase immune system function, and help the body resist infection. Probiotic bacteria are typically found in dairy products such as yogurt and cheese.

Dr. Mohamadzadeh, an associate professor of gastroenterology at Northwestern University’s Feinberg School of Medicine, working along with other researchers, developed an oral probiotic vaccine to be used against anthrax. He is also at work developing a similar vaccine against breast cancer and a number of different infectious diseases.

In the study, researchers compared mice given an oral anthrax vaccine with mice given an injected anthrax vaccine. Following vaccination, the scientists then exposed both groups of mice to anthrax. The researchers found that the survival rate among both groups of mice was the same. Eighty percent of the mice in both treatment groups survived exposure to anthrax following vaccination. The new oral vaccine has yet to be tested on human subjects.

There are several benefits to using an oral vaccine connected with probiotics. First, an oral vaccine is more effective than a standard injection vaccine because it delivers the vaccine directly to the digestive system. (The center of the immune system is found in the small intestine.) When the probiotic bacteria reach the intestines, they colonize and produce the vaccine in the gut. According to Dr. Mohamadzadeh, when a vaccine is sent directly to the gut, “you get a much more powerful immune response than by injecting it.” Another potential benefit of probiotic vaccines is a reduction in side effects, such as injection site pain, nausea, or allergic reactions.

The study is published in the March 17, 2009 edition of the journal Proceedings of the National Academy of Science. The research was funded in part by the National Institutes of Health and the North Carolina Dairy Foundation.

In humans, T cells fight viruses and other invaders. Scientists have long thought T cells simply killed an enemy and then moved on to fight others, but new research suggests that some T cells use the spoils of their battles to win the larger war.

White blood cells are part of the immune system, the human body’s main defense against viruses and other infectious agents, all of which are called pathogens. Pathogens take over the machinery of a cell and cause it to manufacture more pathogens, leading to infection. The body has six major classes of white blood cells, each offering specific weaponry and tactics for combating infection. One class of white blood cells is the lymphocytes, which include T cells and B cells.

Killer T Cells

One type of T cell, the CD8+ T cell, is known more commonly as a “killer” T cell. It attacks infected cells with cytoxins, which cause the plasma membrane of an infected cell to open, allowing water, ions, and toxins to rush in. The infected cell then swells and bursts, destroying the pathogens that have taken over the cell. Until recently, scientists thought that T cells left their victims after killing them and simply moved on to attack other infected cells. Results of recent research, however, show that the interaction between killer T cells and infected cells is more like that of predator and prey.

Slifka and Beadling dyed infected cells with a fluorescent green dye so that these cells could be more easily seen under a microscope. They then unleashed killer T cells that were specific to the virus of the infected cells, to observe their interactions. They watched the small T cells attack and kill the large green infected cells as expected. But Slifka and Beadling noticed something strange. The T cells, which had not been dyed, were themselves turning green as the infected cells broke apart. Slifka and Beadling realized that the T cells were actually eating portions of the infected cells’ membranes. Like a child whose tongue is stained purple from a popsicle, the fluorescent dye was a telltale sign that the killer T cells weren’t just killing the infected cells, they were feeding on them. They had been caught “green-handed.”

A Well-Fed Army

A fluorescent infected cell is killed and partially devoured by killer T cells. (Credit: David Parker and Scott Wetzel/OHSU)

“This is truly a case of microscopic cannibalism,” Slifka says. “And this is the first time we’ve seen virus-specific killer T-cells ingest parts of infected cells.” Slifka thinks that the benefit of this behavior is that T cells can refuel themselves before fighting other infected cells. He compares this to an army of warriors that invades a city, destroys it, but takes care to gather resources that could help it maintain strength in its ongoing war. “Not only do you have this warrior cell coming in and attacking these virus factories, but it’s able to take away nourishment from this in order to help it to continue the fight against the infection,” he says.

A similar response to virus-infected cells by CD4+ T cells, also known as “helper” T cells, was observed by researcher David Parker, also of the Oregon Health & Science University. The value, Slifka says, of these discoveries about T cells is that the same experimental techniques used to study interactions with pathogens could be applied to observe and measure the response of T cells to a vaccine.

Hope for Vaccines?

A vaccine is a substance that carries the identifying markers, or antigens, of a virus but does not have the destructive capabilities of the actual virus. Some vaccines are made from dead viruses. Others are weakened versions of a virus. A vaccine triggers an immune response. The body produces lymphocytes such as B and T cells that will be able to recognize the real virus should it ever appear in the body. In other words, a vaccine teaches the human body how to identify and defeat a virus, but without putting the body through the danger of the real viral infection.

Slifka’s findings suggest that if a vaccine were marked with a fluorescent green dye, and killer T cells were then unleashed to attack and consume the vaccine, scientists could accurately measure the interaction between the vaccine and the killer T cells. This could help determine a vaccine’s effectiveness, as well as the dosage needed to immunize a person.

More to Explore

Check out the following sites to hear from Dr. Slifka, read more about his discovery, and watch killer T cells as they kill and eat an infected cell.